1. Field of the Invention
The present invention relates to a liquid crystal electro-optical device which has a liquid crystal layer composed of a mixture of a nematic liquid crystal material and a liquid crystal material having a smectic phase and which operates, for example, by a twisted nematic mode.
2. Description of the Related Art
Nowadays, a liquid crystal electro-optical device is used in a wide range of fields such as an office automation equipment such as a word processor or a laptop computer, a liquid crystal television, a PDA, a mobile phone as well as a clock or a calculator.
The mode generally used for this liquid crystal electro-optical device is a twisted nematic mode (hereinafter, referred to as TN mode in this specification) in which rubbing treatment is conducted to an orientation film provided for an upper substrate and a lower substrate and rubbing directions of the upper substrate and the lower substrate are shifted by 90° to each other. In case of a TN mode, when an electric field is applied to a liquid crystal from a pair of electrodes, a major axis of the liquid crystal is oriented so as to be perpendicular to the substrate by an interaction of an electric field and dielectric anisotropy. A polarizing plate is used to distinguish a state of a liquid crystal molecule when voltage is not applied to a liquid crystal (twist) from a state when voltage is applied to the liquid crystal.
In a liquid crystal electro-optical device using a nematic liquid crystal which is widely used for a liquid crystal electro-optical device and using a TN mode, for example, response time (sum of rise response time and fall response time) which is mentioned in Patent Document 1 (Patent Document 1: Japanese Patent Laid-Open No. H6-281963) is 20 msec or more. However, in the case of displaying a moving image or the case of employing a field sequential method, this response time is not enough and a liquid crystal material which can conduct further fast response is required.
In the case of displaying a moving image by a liquid crystal television or the like or the case of employing a field sequential method in an operation mode, there is a problem of influencing on visual quality, for example, contrast is lowered or afterimage is generated since response of a liquid crystal does not catch up if response time of a liquid crystal is 20 msec or more in driving a liquid crystal by a TN mode using a nematic liquid crystal material. Although response time of a liquid crystal can be shortened by narrowing a cell gap, there is a limitation on narrowing a cell gap. The term “cell gap” means a thickness of a liquid crystal layer held between two substrates or a distance between the two substrates.